“We believe this to be a murder-suicide,” San Bernardino Police Chief Jarrod Burguan tweeted. “Happened in a classroom. Two students have been transported to the hospital.”

The two dead adults are believed to be the gunman and a teacher. Officials have indicated that the shooter walked into a classroom and shot the teacher, who may have been a former girlfriend, then turned the gun on himself.

“We do not know the age of the students. We do not know the grade that the teacher taught,” San Bernardino City Unified School District spokeswoman Maria Garcia told reporters.